Adds a new JMBE Audio Library preference to the user preferences editor (#489)

so that users can set the library path once and it will persist across
application upgrades so that they do NOT have to copy the library to
their application install with each upgrade.

src/main/java/io/github/dsheirer/preference/decoder/JmbeLibraryPreference.java

@@ -0,0 +1,120 @@
+/*
+ * ******************************************************************************
+ * sdrtrunk
+ * Copyright (C) 2014-2019 Dennis Sheirer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>
+ * *****************************************************************************
+ */
+
+package io.github.dsheirer.preference.decoder;
+
+import io.github.dsheirer.preference.Preference;
+import io.github.dsheirer.preference.PreferenceType;
+import io.github.dsheirer.sample.Listener;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.prefs.Preferences;
+
+/**
+ * Decoder preferences
+ */
+public class JmbeLibraryPreference extends Preference
+{
+    private final static Logger mLog = LoggerFactory.getLogger(JmbeLibraryPreference.class);
+    private Preferences mPreferences = Preferences.userNodeForPackage(JmbeLibraryPreference.class);
+
+    private static final String PREFERENCE_KEY_PATH_JMBE_LIBRARY = "path.jmbe.library";
+    private Path mPathJmbeLibrary;
+
+    /**
+     * Constructs this preference with an update listener
+     *
+     * @param updateListener to receive notifications whenever these preferences change
+     */
+    public JmbeLibraryPreference(Listener<PreferenceType> updateListener)
+    {
+        super(updateListener);
+    }
+
+    @Override
+    public PreferenceType getPreferenceType()
+    {
+        return PreferenceType.JMBE_LIBRARY;
+    }
+
+    /*
+     * Path to the JMBE audio codec library
+     */
+    public Path getPathJmbeLibrary()
+    {
+        if(mPathJmbeLibrary == null)
+        {
+            mPathJmbeLibrary = getPath(PREFERENCE_KEY_PATH_JMBE_LIBRARY, null);
+        }
+
+        return mPathJmbeLibrary;
+    }
+
+    /**
+     * Sets the path to the JMBE library
+     */
+    public void setPathJmbeLibrary(Path path)
+    {
+        mPathJmbeLibrary = path;
+        mPreferences.put(PREFERENCE_KEY_PATH_JMBE_LIBRARY, path.toString());
+        notifyPreferenceUpdated();
+    }
+
+    /**
+     * Resets (removes) the current JMBE library path
+     */
+    public void resetPathJmbeLibrary()
+    {
+        mPreferences.remove(PREFERENCE_KEY_PATH_JMBE_LIBRARY);
+        mPathJmbeLibrary = null;
+        notifyPreferenceUpdated();
+    }
+
+    /**
+     * Returns the path stored in preferences and referenced by the key argument if it exists, otherwise returns the
+     * default path.
+     *
+     * Note: the default path is not checked for existence.
+     *
+     * @param key to the preferences service for the path
+     * @param defaultPath to use if the preferred path does not exist
+     * @return requested path
+     */
+    private Path getPath(String key, Path defaultPath)
+    {
+        String stringPath = mPreferences.get(key, defaultPath != null ? defaultPath.toString() : null);
+
+        if(stringPath != null && !stringPath.isEmpty())
+        {
+            Path temp = Paths.get(stringPath);
+
+            if(Files.exists(temp))
+            {
+                return temp;
+            }
+        }
+
+        return defaultPath;
+    }
+}